1. Technical Field
The present invention relates to an illumination device, a liquid crystal device, and an electronic apparatus and, more specifically, to a relative positioning structure between light sources and a light guide panel in an illumination device having the light sources and the light guide panel.
2. Related Art
In general, an illumination device configured to cause light beams emitted from light sources such as LEDs to enter a light entrance plane configured of a part of an end surface of a light guide panel, propagate in the light guide panel, and go out from a light exit plane of the light guide panel is known. Such illumination device is used as a surface illumination device such as a backlight for illuminating a liquid crystal panel.
In the illumination device as described above, since the luminance distribution of illumination light beams on the light exit plane of the light guide panel varies with the gap between the light sources and the light entrance plane of the light guide panel, the gap between the light sources and the light entrance plane of the light guide panel is set by fixing a light source substrate on which the light sources are mounted and the light guide panel to a holding frame formed of synthetic resin or the like respectively. However, in this configuration, since the light sources and the light guide panel are positioned via the holding frames, the gap varies due to the shape errors of the respective members, and hence fluctuations of the luminance and the distribution of the luminance of the light guide panel may be resulted.
Therefore, in the related art, an illumination device in which fluctuations of the luminance and the distribution of the luminance of the light guide panel is reduced by bringing the light sources into abutment with the light entrance plane of the light guide panel is known (for example, see JP-A-2004-55454). There is also a known illumination device in which a spacer is interposed between the light source substrate and the light guide panel, and the light guide panel is urged toward the spacer for positioning (for example, see JP-A-2006-13087).
On the other hand, an illumination device in which a heat conductive resilient sheets are arranged between the end surface of the light guide panel and the light source substrate and between the light source substrate and a heat sink respectively in order to improve heat discharging property from the light sources to the heat sink is known (for example, see JP-A-2006-64733).
However, the aforementioned illumination device in which the light sources are brought into abutment with the light entrance plane has a problem such that the light sources and the light guide plane may be mechanically damaged when the device is subjected to an impact, or the light guide panel may be changed in property due to heat from the light sources. Specifically, in the case of the illumination device to be mounted to an equipment which is used under an environment which is relatively susceptible to an impact as vehicle-mounted equipment, for example, as will be seen in an oscillation test in which a vehicle-mounted environment is assumed, with the structure in which the light sources and the light guide panel can come into contact with each other, the light sources (LEDs) are subjected to a load little by little, and hence cracking occurs in solder at the mounted portion, so that a defective illumination may be resulted.
The illumination device in which the gap between the light sources and the light guide panel is kept by the spacer may suffer from defective mounting of the light sources as in the above-described case since the light source substrate is applied with a stress (an impact) repeatedly from the spacer due to vibrations applied when being mounted to the vehicle.
Furthermore, in the illumination device in which the heat conductive resilient sheets are arranged between the end surface of the light guide panel and the light source substrate and between the light source substrate and the heat sink respectively, since the heat conductive resilient sheets interposed between the light guide panel and the light source substrate has a thickness slightly thicker than the mounting height of the light sources, the light sources and the light guide panel come into and out of abutment with each other repeatedly upon reception of vibrations and impacts, whereby the light source mounted structure may become damaged. In addition, since the heat conductive resilient sheets are arranged on both sides of the light source substrate, it is difficult to set the position of the light source substrate to a high degree of accuracy, and since the position of the light source substrate with respect to the light guide panel are liable to vary according to the amount of the resilient deformation of the heat conductive resilient sheets on the both sides, there arises a problem that fluctuations of the luminance and the distribution of the luminance may occur.